1. Field of the Invention
The present invention generally relates to fluid injectors for delivering high pressure fluid in a controlled manner. More particularly, the invention relates to an improved fuel injector for supplying fuel to an internal combustion engine, the injector utilizing at least one needleguide. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Related Art
Fuel injection nozzles for supplying fuel to internal combustion engines are well known in the art. Such injectors typically employ an injector body which is affixed to an internal combustion engine such that a nozzle end thereof extends into an engine cylinder. The injector body defines an interior cavity which is fluidly connected with a fuel supply and a needle valve cooperates with the injector body to selectively permit fluid received from the fuel supply to pass through the interior cavity of the injector body and into the engine cylinder. Most internal combustion engines employ a plurality of cylinders and it is common to employ one or more of such injectors with each engine cylinder. Recent developments have focused on supplying fuel to these multiple injectors from a common fuel-supply rail and on controlling the injectors with a centralized microprocessor.
One type of injector described above is shown in FIG. 1, the injector being shown in the non-injection phase of the injection cycle. The common rail injector 10 of FIG. 1 employs a hydraulic force imbalance scheme wherein a power piston 12, disposed at one end of a needle valve assembly 14, cooperates with other components to control the net system forces acting upon the needle valve assembly 14. In the design shown, a control chamber 16 which lies adjacent one end of the power piston 12 contains a volume of high-pressure fuel during the non-injection phase of the injection cycle. The force of this high-pressure fuel acts downwardly on the power piston 12 to urge an opposite end of the needle valve 14 to sealingly engage with an apertured nozzle 22 of an injector body 24. In this state, the fuel supplied to the injector 10 is not permitted to pass into the engine cylinder. However, the pressure within the control chamber 16 can be relieved by energizing an actuator 30 to move a valve 26 and open a spill path 28 from the control chamber 16 to low pressure return 27 thereby decreasing the pressure in the control chamber 16. When the pressure within the control chamber 16 drops to a predetermined level, the needle valve 14 moves upwardly to permit fuel to flow through the injector body cavity 15, through apertured nozzle 22 and into the engine cylinder. De-energizing the solenoid actuator 30 closes the fuel spill path 28. The pressure within the control chamber 16 then increases until it overcomes the upward force acting on the needle valve 14 and needle valve 14 is again urged into its initial position. With the fuel injection cycle thus completed, it can be repeated as desired.
It should be appreciated that the injector of FIG. 1 is normally connected to a microprocessor for controlling actuation of actuator 30 in order to achieve the desired beginning of injection (BOI) and end of injection (EOI) events. In order to provide a feedback mechanism for the injector/microprocessor system, the combination of the electrically-conductive needle valve assembly 14 and the electrically-conductive injector body 24 are used as contacts of an electrical switch which operates as described below. Needle valve assembly 14 is supported within injector body 24 at upper insulating guide 17 and at lower insulating guide 20. Valve assembly 14 is normally urged into contact with apertured nozzle 22 of injector body 24, thus, closing the electrical circuit. An insulating button 18 is located between the upper portion of needle valve 14 and power piston 12 to prevent electrical conduction therebetween. Therefore, needle valve 14 only makes metal-to-metal contact at apertured nozzle 22 and at a compression spring 23. The upper end of spring 33 is supported by an insulated washer and is connected to a BOI/EOI output wire schematically represented at 25. When needle valve 14 physically contacts body 24, a closed electrical circuit is formed between output wire 25 and nozzle body 24. When valve needle 14 moves away from apertured nozzle 22, the electrical circuit is broken. Thus, opening and closing needle valve 14 opens and closes the electrical circuit which signals the beginning and end of injection (BOI/EOI).
Upper and lower insulating guides 17 and 20 are of a conventional nature. These insulating guides can be formed by coating either or both of needle valve assembly 14 and injector body 24 with some wear-resistant insulating material such as diamond-like carbon (DLC) or aluminum oxide. Additional methods of forming upper and lower insulating guides 17 and 20 are disclosed in U.S. Pat. No. 4,066,059 to Mayer et al granted Jan. 3, 1978 and U.S. Pat. No. 4,414,845 to Hofmann granted Nov. 15, 1983. The contents of these patents are hereby incorporated by reference.
While injectors of the type shown in FIG. 1 are effective for their intended purpose, such injectors suffer from a number of deficiencies directly associated with the nature of conventional insulating guides 17 and 20. First, insulating guides 17 and 20 are prone to excessive wear during long-term use due to the relative movement between needle valve assembly 14 and injector body 24 during injector cycling. This is particularly true when insulating guides 17 and 20 are formed by directly coating either or both of needle valve assembly 14 and/or injector body 24 with an insulating material. A second deficiency is that coating selected portions of needle valve assembly 14 and/or body 24 with insulating materials can add unnecessary expense to the cost of an injector. Similarly, where insulating guides 17 and/or 20 are formed using insulated inserts, injector assembly costs can add additional costs. A third deficiency associated with conventional injectors resides in the need for high quality control standards associated with manufacturing and utilizing conventional insulating guides. In particular, high quality control standards must be applied in utilizing conventional insulating guides 17 and 20 because even a small defect in an insulating guide can cause failure of a fuel injector. Such a failure could either occur due to initial manufacturing defects or due to long term wear on the insulating guide. Yet another deficiency associated with injectors utilizing some conventional insulating guides is that they do not permit the flow of fuel between needle valve assembly 14 and body 24 in the region of the guide. While this characteristic may be desired in some instances, it impedes performance of the injector in other instances.